
#pragma warning(disable:4996)
#include<stdio.h>
#include<math.h>
int main()
{
    double a, b, c, s, p;
    scanf("a=%lf,b=%lf,c=%lf", &a, &b, &c);
    p = (a + b + c) / 2;
    s = sqrt(p * (p - a) * (p - b) * (p - c));
    printf("s=%.4lf", s);
    return 0;
}